This Program Project Grant is concerned with the developmental biology of the lung. It deals with an important but poorly understood area of lung biology related to regulation of differentiation of alveolar epithelial cells during embryonic, fetal and early postnatal life. We will apply a broad panel of markers for the differentiated phenotypes of alveolar type 1 and type 2 cells that we have developed or are characterizing in our laboratories, to multidisciplinary studies which examine the transcriptional and translational regulation of expression of these differentiation-related genes at organ, cellular and molecular levels. Our experimental systems include embryonic and fetal lungs, isolated lung epithelial cells, molecules and genes. Our ungoing studies of lung development have raised questions about existing concepts of alveolar epithelial cell differentiation and have allowed us to pose a number of new hypotheses regarding timing, lineages, and regulatory mechanisms of alveolar epithelial cell differentiation. The proposal involves a number of investigators who have been working in developmental biology of the lung for some time and adds investigators with experience in other model systems of development. The program consists of four focused projects which are designed to be highly interactive, supported by two scientific and an administrative core. Project I focuses on timing and spatial patterns of gene expression in embryonic and fetal lung and analysis of factors which may modulate this process. Project II, using isolated fetal lung epithelial cells and two immortalized type 2 cell lines developed in our laboratories, examines biologic and molecular mechanisms which regulate expression of the above panel of genes. Projects III deals with molecular regulation of expression of several genes identified in proliferation-arrested type 2 cells and examines mechanisms of proliferation arrest in these cells. Project IV will utilize the embryonic lung to investigate epithelial cell lineage. the process of cell determination and the expression of genes which may effect the positional patterns of cell differentiation studied in Project I. The work proposed will provide new concepts of alveolar epithelial cell differentiation and new information of the regulation of gene expression and functions of the cells which form the gas exchange surface of the lung.